Problem: Last Monday, Ben's parents gave birth to twins and named them Luis and Stephanie. When they were first born, Luis weighed 8.98 pounds and was 18.5 inches tall, and Stephanie weighed 6.21 pounds and was 18.5 inches tall. How much did the babies weigh in total?
Explanation: To find the weights of the 2 babies, we need to add their weights together. Luis's weight + Stephanie's weight = total weight. ${8}$ ${9}$ ${8}$ ${6}$ ${2}$ ${1}$ ${+\vphantom{0}}$ ${9}$ ${1}$ ${5}$ ${1}$ Together, the babies weigh 15.19 pounds.